Low alloyed steel is a material which, in general, is difficult to machine with coated or uncoated cemented carbide tools. Smearing of workpiece material onto the cutting edge and flaking of the coating often occur. The cutting condition is particularly difficult when intermittent machining is employed under wet conditions (using coolant).
When machining low alloyed steels with coated cemented carbide tools, the cutting edge is worn by chemical wear, abrasive wear and by so-called "adhesive" wear. The adhesive wear is often the tool life limiting wear. Adhesive wear occurs when fragments or individual grains of the coating possibly followed by parts of the cemented carbide are successively pulled away from the cutting edge by the workpiece chip as it is formed. Further, when wet cutting is employed the wear may also be accelerated by an additional wear mechanism. For instance, coolant and workpiece material may penetrate into the cooling cracks of the coatings. This penetration often leads to a chemical reaction between workpiece material and coolant with the cemented carbide. The Co-binder phase may oxidize in a zone near the crack and along the interface between the coating and the cemented carbide. In time, coating fragments are lost piece by piece.